Movement and position measuring device and method

ABSTRACT

A method and a device for detecting a position of a graduation support relative to a support of the device in a direction of displacement of the graduation support and the support relative to each other. The device has a light source. The support has a high resolution graduation consisting of a sequence or array of optical elements focusing the light beam sensing plane on a support on which light-sensitive sensing elements are arranged so that the displacement of the graduation support in relation to the sensing plane can be assessed with precision. The light flux is modified by the graduation and intercepts at least the entire width of an optical element such that the light energy is converted into an alternating signal representing the position of the graduation support in relation to the support. The device is suitable for producing high resolution sensors with simple elements which are easy to manufacture.

BACKGROUND OF THE INVENTION

The invention relates to a method and/or device to detect with the aidof a light beam the relative or absolute position on the displacementaxis of a graduation support in relation to a support belonging to adevice, which includes:

a light source producing a light flux,

a graduation support having a graduation placed in the light flux whichit modifies,

a support containing one or several sensitive elements capable ofintercepting the modified light flux,

one or several sensitive elements which convert the intercepted lightintensity into a physical effect,

and a detection circuit suited to produce a useful electric circuit forthe design of movement and position sensors.

EP Patent application 474 149 A2 (Kawamura) describes such a device inthe form of an incremental encoder. The working principle ischaracterised by the fact that the graduation is made out of atransparent half-division and a focusing half-division to which twosensitive diodes correspond to the light of a width equivalent to ahalf-division. The level of resolution reached by the device is notquantified.

The dimension of the light spot is defined as infinitely small and thenon-illuminated zone as dark. This point of view holds as long as theoptics are perfect and the effect of diffraction are not apparent.

The working of the device depends on, among other things, the dimensionof the light spot projected by the focusing part on the detectiondiodes. For example, for a lens of 20 μm and a focal distance of 80 μmwhich corresponds to the dimension of 40 μm of a division, the width ofthe light spot corresponds to 30% of the width of the sensitive element.The current curves described in the Kawamura's patent are no longerusable, in particular the resolution can not be multiplied as specified.

The unit resolution of the device corresponds to an alternation of thedigital signal for a division length. The sensor's resolution is definedas the graduation's resolution.

The unit resolution corresponds to the resolution defined by thegeometric and physical layout of the sensitive elements. The graduationresolution corresponds to the resolution defined by the dimension of agraduation's division.

Another disadvantage of this device lies in the fact that the form ofthe position signal is not in tune with current technology which is anhandicap to the product's commercialization.

Furthermore, the Kawamura disclosure doesn't report the constraintsrelative to the creation of the light source. It also doesn't mentionpreferential forms of the lens for improving the device's resolution.

Patent EP 0206 656 (Leonard) describes a device which works with agraduation made of elements having a first half-portion to let the lightpass through and a second half-portion to retain the light. Aminiaturisation of the graduation support is limited, either formechanical construction considerations or for the high costs related tothe making of a glass graduation using lithographic techniques.

Patent EP 0489399 A2 (Igaki) uses a series of optical elements arrangedon a cylinder and a light flux crossing the same graduation twice. Onthe first crossing, half of the light flux is reflected and the otherhalf is modified by grating effect and projected on the opposite side ofthe graduation where the light flux is divided in three directions. Thepossible resolution depends on the wavelength and the graduation-supportdiameter defined by the formula:

(N−¼)*(graduation pitch)*(graduation pitch)/(wavelength)<graduationdiameter<(N+¼)*(graduation pitch)*(graduation pitch)/(wavelength)

This means that 15 mm diameter corresponds to a resolution ofapproximately 760 divisions. The commercial product claims a resolutionof approximately 80′000 divisions which requires a complex circuitdetector for the treatment of the signals generated by three receiverdiodes. The design of the graduation support as a cylindrical graduationonly doesn't allow, for example, to design a level sensor.

The U.S. Pat. No. 4,531,300 shows an example of a level-measurementdevice which uses an identical technique to that of Leonard. This deviceis particularly cumbersome and too costly to compete with the standardbubble-sensor products. The use of capacitors or magnetic-resistantsensors requires an analog/digital circuit converter of higher than12-bit resolution which is more difficult to conceive than apurely-digital circuit.

Patent PCT/EP 93/02415 describes a kilometer measurement systemrequiring a sensor for the measurement of the movement dynamics of avehicle. The use of a gravitational sensor is favorable for its stablefunctioning over time and its simplicity of use. The values to bemeasured require a high-resolution sensor which is not available on themarket.

With the devices described above it is not possible to conceivesmall-sized absolute sensors based on a linear-code reading as describedin the patent JP 3-6423 (15). There is also not possible to conceivehigh-resolution gravitational sensors that certain market applicationsrequire.

SUMMARY OF THE INVENTION

It is an object of the present invention to apply a new method anddevice which allow the state-of-the-art deficiencies to be circumventedin order to considerably improve the performance, in particular theresolution, of the function related to the incremental or absolutemeasurement of a displacement.

Other objects of the invention are the improvement of the electricalcharacteristics of this type of device, in particular the currentconsumption and reduction of production costs.

The above objects of the invention are attained by a method and devicefor detecting one of the relative and absolute position on adisplacement axis of a graduation support of the device with the aid ofa light beam, which device comprises a light source producing a lightflux, a graduation support including a graduation placed in the lightflux which it modifies, a support containing at least one lightsensitive element capable of intercepting the modified light flux, saidat least one light sensitive element converting the intercepted lightintensity into a physical effect, and a detection circuit suited toproduce a useful electric signal, the graduation support containing atleast one graduation made of at least one of several series of opticalelements, said optical elements containing at least one focusing portionwhich focuses the light flux on the support containing the lightsensitive elements and which produces several light spots. The lightspots may be in one of an oblong and rectangular shape and may bearranged perpendicularly to a median line of the graduation. During arelative displacement between the graduation support and the support adistance equal to a length of a division, the maximum overlapping oflight energy by at least one of said light spots belonging to the sameoptical element of said at least one of said light sensitive elementscorresponds to a portion of one of the minimal and maximal value of analternating signal corresponding to a division and convertible to one ofa digital signal and a position signal.

The method and device of the present invention differ from the methodand device described by Kawamura in that the combination of a singlelight spot with at least one sensitive element is used for the creationof an alternating signal which represents the displacement of thegraduation support in relation to the support containing the lightsensitive elements. A preferred design of the device includes agraduation made of cylindrical lenses placed side by side. In this case,all of the energy crossing the graduation can be focused on one orseveral sensitive elements. A preferred layout of the sensitive elementscorresponds to a series of elements whose width in regards to the medianline is inferior to the length of the division. A higher unit resolutionof the one defined by the division of the graduation can be obtained.The detection circuit can be simplified using a high unit resolution.

The invention's advantage gives the possibility of conceiving an opticalbarrier displacement measurement system working under optimalconditions, this with divisions of large dimension as well as withdivision which dimension correspond to the function limits of focusingelement. The possibility of increasing the unit resolution in relationto the graduation resolution allows the use of each technological aspectin an optimal fashion.

The cylindrical shape of the lens gives the possibility to reduce thelight spot width to a minimum and to size the length of the lens toinsure the propagation of sufficient light energy. It also gives thepossibility to design in a elegant manner a graduation adapted to thedesigns of absolute measurement devices. The oblong shape of the lightspot, which is common to cylindrical lenses, is also well adapted to thedesign of the device described in FIG. 10 a.

The invention gives the possibility to design economical sensors of avery high resolution and/or small dimensions. As a result of the lenses'small dimension and the fact that the light source can be placed veryclose to the graduation support, it is possible to design sensors ofsmall axial dimension.

The following example of a design gives a better description of theadvantages of the invention over standard practice.

Supposing there is a graduation made up of lenses with the width of 16μm having a focal distance of 80 μm which is combined with sensitiveelements of the width of 4 μm and the length of 200 μm. The width ofthese elements corresponds to the division length of a 16 μm. This setupresults in 3000 divisions placed on a 15.3 mm diameter. The modulationof the light flux is such that the minimal possible width “M” of thelight impact on the plane of the sensitive elements measuresapproximately 3 μm. The use of 4 diodes of the width of 4 μm for onedivision gives the possibility with a differential evaluation of thecurrent to bring the resolution up to 6000 divisions. A second group ofsensitive elements shifted by a division of ¼*¼ give the possibility toproduce a signal as a cosine shape. A simple detection circuit canmultiply the unit resolution by 4 and bring up the resolution up to24′000 units. A detection circuit and a mechanical device of goodquality open the possibility to multiply the unit resolution by 256 andbring up the resolution to 153,600 divisions. The choice of focaldistance of 40 μm combined with a carefully designed mechanics of theelements being part of the device allows the resolution of the aboveexample to be doubled.

Using the device put forward by Kawamura alike the above example, thedivision of the graduation should be of 8 μm, that is, a lens of 4 μm,which cannot be designed since the focal distance of this element shouldbe between 1 and 2 μm to generate a light spot which is sufficientlysmall. Furthermore, the ratio of the current signals generated by thesensitive elements is for a spot infinitely smaller of 8. These twovalues show that the Kawamura's device does not function at such valuesof resolution. The Kawamura's device allows a unit resolution to beapproximately 10 times smaller than the invention. According to theproof set out in FIGS. 4 a-4 d, it can be concluded that with an equalunit resolution, a similar light flux, and with ideal workingconditions, the present invention can produce an electric signal of avalue 8 times higher than the signal produced with the Kawamura'sdevice.

The analysis of the device, according to Leonard, shows that such adevice would reach resolution values of 2 to 4 times lower, for asimilar quality design to 3 to 4 times lower than the device of thepresent invention. A graduation of a similar resolution requires a 8 μmperiod grating whose production is not economical.

The example cited above shows that the current technology does not givethe possibility to reach unit resolutions equal to those of the presentinvention. The experiments carried out to this day have shown that itwill be possible to manufacture graduations, using the invention, of adivision length equal to 8 μm without special techniques.

The graduation can be manufactured by plastic injection moulding whichgives the possibility to produce the graduation support in the sameoperation. The attaching of additional construction elements, forexample a mounting aid, can be achieved without a noticeable increase inthe production cost.

The layout of the sensitive elements according to the invention givesthe possibility to generate with a pair of sensitive elements analternating signal whose value or shape is independent of the light fluxintensity. The sensitive elements can be distributed on severaldivisions. For an optimal position of the light source or an optimalratio between the width of the light spot and the width of the sensitiveelements a sinusoidal signal can be integrated for a higher resolutionof the device. A preferred shape of the optical element is a cylindricallens.

A graduation may be made of different optical elements, each divisionbeing capable of being assigned a numerical value which can define theabsolute position of the graduation support. Absolute encoders may bedesigned with the equal dimensions as those of the sensors describedabove. This technology, which can be achieved by the use of cylindricallenses, holds particular advantages for the fabrication of small-sizedabsolute encoders.

The detection circuit may be integrated with the sensitive elements onthe same support which will also be the case, for example, for a 13-bitabsolute resolution sensor. The circuit will be small sized andeconomical.

As a result of the characteristics described above, the presentinvention provides the possibility to design new products which aresimple and function with few elements, which cannot be realized by theprior art technology. Sensors may be produced, which are economical,which have high resolution, which are of small in size, which use littlepower, which can deliver incremental impulses and/or absolute positionvalues and which will be adapted to the future of micro-electronics inwhich the trend is toward miniaturisation and energy efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are used for the explanation of the invention:

FIG. 1 is a simplified diagram of the measuring device;

FIG. 2 shows an electric signal in relation to the light signal;

FIG. 3 shows a disposition of the elements of the device of FIG. 1;

FIGS. 4 a-4 d show a comparison of the performances between thisinvention and prior art;

FIG. 5 is a preferential design for the graduation;

FIGS. 6 a-6 d shows a focusing portion;

FIG. 7 shows an alternative design of the measurement device;

FIG. 8 shows another alternative design of the measurement device;

FIGS. 9 a-9 c show layouts of the sensitive elements;

FIGS. 10 a-10 d show a disposition of the sensitive elements and shapesof a signal generated;

FIGS. 11 a-11 d show a numerical value graduation;

FIGS. 12 a-12 b show an example of a linear detection code;

FIGS. 13 a-13 b show a graduation support for an encoder;

FIG. 14 is a circuit for an absolute encoder;

FIGS. 15 a-15 b shows synchronization of the position signals;

FIG. 16 is an example of a neuronal circuit;

FIG. 17 shows oscillations and procedure for detection;

FIGS. 18 a-18 f show a disposition of the light source;

FIG. 19 shows gravitational sensors;

FIG. 20 shows a friction bearing;

FIGS. 21 a-21 b shows a low-friction bearing; FIG. 22 shows anoscillating disc;

FIG. 23 shows an electronic level measurement device;

FIG. 24 is a unit diagram for an odometer; and

FIG. 25 shows an encoder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The light source is the part which consumes the most current, it'stherefore advantageous to use this energy in an efficient manner.

A sensitive element which corresponds to an integrated diode in a CMOStechnique has an internal capacity which defines the working limit infunction to the current emitted by the sensitive element and the currentlevel capable of being used by the detection circuit. This capacity alsowill define the minimal threshold of the required luminosity and/or themaximum displacement speed of the support in relation to a sensitiveelement. The capacity value for the diode mainly depends not only on itssurface, but also on the technique used for its manufacture.

Focusing the light flux gives the possibility to increase the level oflight energy received per unit of surface, to reduce the surface and theinterference capacity of the sensitive element.

The use of small-dimensioned optical elements gives also the possibilityto reduce the axial dimension of the sensor. An equal ratio between thedistance separating the light source from the optical element and theoptical element's width corresponds to the same intensity of usefullight flux for the detection process.

Using small-dimensioned optical elements gives also the possibility toreduce the dimension of the sensitive elements thus enabling theintegration of the detection or reading function onto the same supportor chip.

The manufacture of optical or graduation elements can be achieved byelectron beam manufacturing. An X-Y table at a nanometer resolution canmanufacture high-quality optical elements on the basis of binary datacharacterising the geometric shape of the optical element.

A point or section of the electron beams is positioned on the part to betreated along the X-Y axis. The Z axis is obtained by modulation of theintensity of the electron flux.

By taking out or modifying the material, this method allows to machinedifferent materials such as polymers, in particular polycarbonate,quartz, and steel which can be used in the manufacturing of plastictools or other materials. When polymer is used a copy of the originalshape will be manufactured by electrolytic deposit of Nickel or otheralloys. The obtained part can be for example placed in an injectionmoulding tool. This process allows the making of variously-shapedgraduations such as are described in this document.

Referring now to the drawings in detail, and firstly to FIGS. 1-3, FIG.1 shows the disposition of different elements being part of the device,which are shown schematically as a section. The device includes a lightsource 1 of width, dimension or section S 101, a lens or an opticaldevice 2 for a better modulation of the direction of the light fluxschematically represented by 13, a section of the graduation support 3containing a series of cylindrical optical elements 4 of width E 21containing a focusing portion, which portion may focus the lightradiation represented by lines 12 and 13 on the image plane 7 onto aspecific point named light spot 11 of dimension B 10. Light-sensitiveelements 6 of width or dimension R 9 are part of the support 8. Thelines 18 delineate the division. The lines 17 represent the geometricaxis of the division which in this case corresponds to the optical axisof the optical elements 4. The graduation support 3 can be displacedhorizontally in the direction of arrow 25 in relation to the sensitiveelements 6. The dimensions c 14, a 15 and b 16 define the position ofthe elements in relation to the graduation, and the final planerepresented by a dashed line 5, which corresponds to a line beyond whichit is no longer possible to reduce the dimension of the image projectedonto the image plane 7. The curve 24 represents the distribution oflight intensity on the image plane 7. It is characterized by the twodimensions M 20 and L 19. The image of the electric signal obtained bythe displacement 25 of the graduation support 3 in relation to support 8is represented by signal 22, maximum value 22 a or minimum value 22bwhich crosses a reference value at least two times. A central positionof the light spot 11 in relation to a sensitive element 6 may correspondto a maximal signal value 22 a or a minimal signal value 22 b. Thissignal can be converted into a useful digital and/or analog signal 23. Alogical value of the digital signal 23 can corresponds to a positionsignal.

The light source 1 should preferably be a diode of an elongated shapewhich is represented here in section. A width of 20 to 200 μm can berepresentative for the device. It can correspond to a laser or someother light source which emits in the range of UV, of visible light, ofinfrared or other. The optical device 2 can make the direction of thelight flux crossing the graduation to be parallel. The device can alsobe conceived without the optical device 2.

The light beam 13 defined by the optical element 4 is focused on theimage plane 7 onto one point, represented by a light spot 11. The widthB 10 of the light spot 11 is less than the projection of the opticalelement 4 section on the image plane 7. One or several light spots 11can correspond to an optical element.

The energy-converting or light sensitive elements 6 can be diodes oftype P+/N or of any other type which are compatible with CMOStechnology, photo-transistors or other elements which can convert theenergy from the light source into current and/or vary the physicalcharacteristics of the sensitive elements. They can be placed on thesame geometric plane and be integrated into the same support 8.

A group of sensitive elements is represented by the combination ofsensitive elements 6 a and 6 b or, in the case of FIGS. 9 a and 9 c, 6 aand 6 b or 6 c and 6 d. A group of sensitive elements represents thesensitive elements which can create an alternation of the signal 22. Agroup of sensitive elements can also include one single sensitiveelement combined with a reference value which is, for example, generatedby the circuit. In this case, the sensitive element will give ahalf-alternation of the signal 22, from which will be generated ahalf-alternation of the digital signal 23.

A unit of sensitive elements 56, 57 (FIG. 9) corresponds to one orseveral groups of sensitive elements allowing the formation of one orseveral alternations of signal 22. By definition the digital signal 23coming from a first unit of sensitive elements corresponds to an outputor channel “A”. A second signal coming from a second unit of sensitiveelements producing a preferably identical signal and shifting by ¼alternation in regards to signal 23 corresponds to an output “B”. Thesubsequent evaluation of channels “A” and “B” enables to detect thedirection of the displacement and to increase the unit resolution of thedevice.

The dimension B10 of the light spot 11, which is very much less than thelength 21 of the division, gives the possibility to increase the unitresolution of the device.

The support 8 can represent a chip or a silicon support of an integratedcircuit to which the sensitive elements and preferably the detectioncircuit are integrated. The detection circuit can convert the currentemitted by the sensitive elements into signals and/or information usableby other electronic devices. A graduation can correspond to severalsupports 8.

By definition, the graduation is a series of optical elements includinga focusing portion which focuses the light onto an area of the support8. If an optical,element corresponds to two light spots, by definition,it will be a matter of two graduations which could be merged or twodifferent divisions.

The dimension S,101 is the width of the light source 1. The dimension B,10 depicts the useful width of the light spot on the image plane 7. Thedimension a,15 is the distance between the light source and/or the lightobject and the optical device 2 which corresponds to preferably thefocal distance of the optical device. The dimension c,14 is the distancebetween the final plane 5 and the optical device 2. The dimension b,16which can be equal to the focal distance f, represents the distancebetween the optical elements 4 and the image plane 7. The dimension G,21is the length of the division or the width of the optical element 4. Thedimension R,9 is the width and/or the average width of the sensitiveelement 6. The dimension L,19 is the first order minimal dimensioncorresponding to the maximal optical resolution of the focusing part.The dimension M,20 is the useful width of the light signal whichcorresponds to a maximum relative energy concentration in regards to therest of the obtained light signal. For example, the light source 1 canbe sized in relation to the useful width.

The relation between the width of the light spot 19 and the width of thelight source 1 is obtained by the formula S/B=a/b. The minimal width ofthe light spot corresponds to the formula Lmin=cl*Lambda*b/E, where clis a value of 2.22 and corresponds to the second maximum lightintensity, where Lambda represents the light's wavelength, where b isthe focal distance and E is the width of the focusing element 4. Thevalue of c 14, which is a limiting value, can be expressed by thefollowing formula: c=M/L*S*E/(cl*Lambda). For values where a>c the widthL or M will remains constant. For values where a<c , the width of thelight spot will vary in function of the relation between the values aand c. Varying the distance a in the a<c domain makes it possible tovary the width M and to act upon the relation R/M and also on the shapeof the electric signal 22.

From the statements made above, it can be concluded that the choice ofthe focal distance of the focusing elements 4 will be the determiningfactor for a maximal energy output. A small focal distance correspondsto L value or minimal M value. For a given width of the light source 1and a given width of the sensitive element R, this allows the lightsource 1 to be moved closer to the graduation support and thus tocapture as much light energy coming from the light source as possible.It also follows that it is more advantageous to use the light source 1working in, for example, blue or green light than in infrared, thecritical dimension Lmin being smaller.

The distance between the optical device 2 and the graduation support 3plays a secondary role. Without the optical device 2, the dimensions 15and 14 will have the optical or focusing element 4 as their origin andthe optical axes will be convergent toward the light source 1.Therefore, there will be a distorted distribution of light spots 11 onthe image plane 7.

The image plane 7 can correspond to the focal plane of the optical orfocusing elements 4,31. Experience has shown that the optimal imageplane is a distance between 1 and 1.2 * the focal distance of thefocusing elements.

The image plane 7 can also correspond to a more distant plane with themaximal illumination obtained by the superposing of the effects due tothe geometric optic and diffraction optic physical laws.

FIGS. 2 a and 2 b give the possibility to visualize the importance ofthe R/M ratio by showing two extreme situations side by side in FIG. 2 awhere the ratio “R/M>1” and in FIG. 2 b where “R/M<1”. A pair ofsensitive elements 6 a and 6 b are represented on the image plane 7.They receive a signal of light intensity designated at 24 and generatewith the help of a non-represented circuit an electric signal 22. Forexample, the sensitive element 6 a produces a current corresponding to apositive value in function with the received illumination and thesensitive element 6 b produces a current of negative-value in functionof the received illumination. The difference of the thus generatedvalues, which can also correspond to the difference of the currentsemitted by the two sensitive elements, corresponds to a signal value 22which periodically varies in function of the displacement of thegraduation support 3.

By using a second group of sensitive elements shifted by a ¼ division,it will be possible to generate two signals corresponding to a sine anda cosine. The transfer of these two signals on a orthogonal plane allowsa vector 26 to be defined whose value will vary in relation to the curve27 during the displacement of the graduation support in relation to 25.The of the vector is represented by 28.

With the ratio R/M>1, the shape of the curve 27 comes closer to that ofa square as shown in FIG. 2 a, a diamond-shape for a ratio of R/M<1, anda circle for a ratio of R/M=1 (not shown).

The stable shape of the curve depends on mechanical and geometricalfactors of the device as well as the working quality of the receiverdiodes. A stable curve gives the possibility to extract the value of theposition angle 28 in a more or less regular fashion.

The quality of the shape of curve 27, which in the best case correspondsto a circle, enables to have an electric measurement which correspondsto an exact position measurement. For example, a curve such as isrepresented in FIG. 2 a causes errors in terms of the definition of thegeometric position.

These two qualitative points of view will determine the capacity of thereal resolution of the measurement system which could be higher than theunit resolution of the device, usually a value of 4 to 256 times higher.

The ratio M/R depends on the ratio a/c being characterised by the shapeand dimension of the light source 1. The relation between a and c willbe a/c>1. a/c>1 corresponds to the width of an unchanged image and aloss of light energy from the fact that the opening angle of thefocusing element is needlessly reduced.

FIG. 3 represents a three-dimensional view of one of the preferredlayouts of the device's elements, that is to say a partialrepresentation of the graduation support 3 limited by line 38, agraduation 30 formed by a series of divisions or optical elements 4aligned on the directrix or median line 32 of the graduation andincluding a focusing portion 31, an image plane 7 corresponding to thesupport area 8 containing the sensitive elements 6 of width 9.

The lines 33 represent the perimeter of the projection of the surface ofoptical elements or of a division on the image plane 7 after the lines18, the section 34 the projection of the focusing portion 31 of width 35and the intersection surface 37 the intersection between the surface 34and the surface of the sensitive element 6 of width 9. The width 35 ofthe projection of the focusing portion 31 will be greater than the width9 of the sensitive element 6 so that signal 22 can be conditioned in thedesired shape.

The sensitive element 6 can be positioned in a perpendicular manner inregards to the median line 32. It will preferably be of an oblong ormainly rectangular shape which, assuming the same manufacturingtechnique is used, gives the possibility to increase the level of lightenergy convertible by a unit of width 9 of the sensitive element 6and/or to increase the resolution of the device for the same amount oflight energy. The width of the sensitive elements can be 2 μm or more.The total value of the width of each sensitive element belonging to thesame division is preferably equal to or less than the value of thelength of the division. Another possible design of the sensitive elementis shown in Fig 11 d.

A principally rectangular shape is understood to be like a surfaceeasily capable of being superimposed on a rectangle or which, in thedirection of the width 9, includes at least two sides of any parallelshape or shape that is converging parallel toward the center of thecurve of the median line 32 and in the sense of the width of two sidesof any shape.

FIGS. 4 a-4 d show a comparison of techniques of the present technologyand of the invention based on the fact that each device has the sameunit resolution and that the light flux is identical. This reasoningalso holds for spherical or cylindrical-shaped lenses. FIGS. 4 a, 4 b,and 4 c represent the disposition of the graduation support fordifferent technology and two schematic diagrams of the positions of thedivision 4 laid out at a distance equal to ¼ of the unit division.

FIG. 4 a shows the present invention. State-of-the-art technology isshown in FIG. 4 b for the Kawamura invention and in FIG. 4 c for theLeonard invention. The lens in FIG. 4 a covers a surface area equal tofour diode widths. A value higher than 4 diodes would also be possiblesince the dimension of the light spot can easily be reduced up to thevalue limits which are approximately equal to M=4*lambda*f/E.

FIG. 4 d shows the shape and the intensity value of the currentgenerated by the sensitive element. Curve 39 a, here in a trapezoidalshape which is due to the reduced dimension of the light spot, depictsthe intensity value for FIG. 4 a, curve 39 b and 39 c the intensityvalue for FIG. 4 b, curve 39 b the intensity value for FIG. 4 c. Thesignal intensity for FIG. 4 a, 39 a corresponds to the value of 4, forFIG. 4 b, 39 b corresponds to 1 and 39 c corresponds to approximately0.8, and for FIG. 4 c to 1.

The shape differences in curves 39 b and 39 c give an idea of what thedeterioration of the signal due to the width of the spot light canrepresent. The ratio of the width of the light spot and the width of thedivision is approximately equal to: B/R=2.22*Lambda*f/E*E For example,for a value of E=20μm and f=80μm, the recovery is equal to 30% of whatthe curve 39 c approximately corresponds to. The shape of this curveshows that the device proposed for an increase of the resolution throughevaluation of the produced electric signal can no longer be applied inthe case of the curve 39 c.

It must be pointed out that the size of the alternating signal generatedby the combining of both sensitive elements 6 a and 6 b enable to reachan amplitude of alternating intensity of:

a factor of 8 for FIG. 4 a

a factor of 1 for FIG. 4 b under ideal conditions

ba figure of 2 for FIG. 4 c

It is clearly evident that, for an equal unit resolution, theinvention's solution ensures a signal of a value much higher than thatof present technology. It should however be noted that the shapes of thecurves 39 also depends on the quality of the shadow zones. Curve 24 inFIG. 1 represents a real measurement of a 16-μm lens and gives an ideaof the illumination ratios encountered.

The formulas used in the calculation of the dimension of the light spotdon't take the grating effects into consideration. Experience has shownthat these values were correct.

FIGS. 5 and 6 a-6 d show different types of optical element. FIG. 5shows a part of the graduation support 3 having a graduation 30 made ofa series of optical elements or divisions 4 of which the focusingportion is made of cylindrical optical elements superposed to thedivision 4 of length 21 and of width 40 which can be alignedperpendicularly to the median line 32. The lens will have, for example,a width E 35 of 8 μm or more, a focal distance of a value between 2*Eand 6*E and a length value between 50 and 600 μm. They correspond to alinear or essentially linear focusing portion.

The optical elements 4 or the focusing parts 31 can be made of the samematerial, preferably plastic which allows the graduation support to beproduced at the same time as the optical elements, i.e. by injectionmoulding.It is also possible to shape the graduation by pressure of atool on a rough shape of the graduation support. Many materials can alsocome into the design of the graduation support.

The graduation support 3 can have many different shapes and includegeometric parts to simplify its assembling onto the device. The samegraduation support 3 can have one or several graduations 30 comprisingoptical elements which are different and of the same type. The medianline 32 can be a circle. It can correspond to the direction of themovement of the graduation support to a given point.

FIGS. 6 a-6 d show various possible designs of the optical element 4having width 21 and length 40 which can include a focusing portion 31which generates an irregular distribution of the light intensity on theimage plane 7 in such a manner that the corresponding part at a highintensity can be defined by one or several light spots 11 which willpreferably cover an oblongand/or mainly rectangular-shaped surface ofthe image plane 7. It corresponds to an essentially linear focusingportion.

The projection of the focusing portion 31 onto the graduation support 3can be an oblong and/or principally rectangular shape.

A linear distribution of the light spots allows the light flux to bedistributed in an optimal or selective manner on the sensitive elements6.

FIG. 6 a shows an optical element 4 of width 21 and length 40 with afocusing portion 31 of a biconical shape shaped by a conical volumewhose focal value will be different from one point to another along thedivision, FIG. 6 b with a cylindrical shape covering from one end to theother the optical element 4, FIG. 6 c with a pyramidal shape with foursides recovering optical element 4 from end to end, FIG. 5 d with apyramidal shape with rounded tips only covering a part of the opticalelement 4.

The cylindrical or pyramidal-shaped surfaces can represent a closegeometrical shape or an asymmetric shape better adapted for the desiredoptical characteristics. In the case of a circular graduation, the shapeconverges toward the center of the graduation curve; in the scope of adivision for numerical value this shape will be asymmetric with regardto the optical axis 17.

A pyramidal form can include two rounded sides which enable over acylindrical shape to design a light spot, which variation of dimensionis less sensible to the variations of the distance between the support 8and the graduation support 3.

The possibility of rounding the lens shape, for example into acylindrical shape directed after the length 40 offers the additionalpossibility of concentrating more energy on the light spot or reducingthe length of the light spot in the direction of the width 40 of theoptical element.

The above examples can also include a Frensel-, binary- and/ordiffraction-type lenses. Binary-type lenses have the disadvantage thatthey are both convergent and divergent, which generates the lightintensity onto the focal point at a value of 50% in comparison to thatwhich is obtained with a geometric lens. Pure diffraction type lensespresent another possible form of execution.

FIG. 7 shows a special disposition of the device. The light source 1corresponds schematically to a diode 1 before which an opaque mask isplaced which allows the dimension S 101 of the source or the lightobject to be defined. The light beams 13 are directed by an opticaldevice 2 onto the graduation support 3.

The configuration of the receiving system includes an optical device 47which gives the possibility to cast the image plane 7 onto the plane ofthe support 8 comprising the sensitive element 6 placed further awayfrom the graduation support 3. This arrangement gives the possibility todesign a device whose mechanical gap 48 is higher than the distance b16, which can correspond to the focal length of the optical elements 4.

The mechanical parts can be freely disposed. A minimal focal distancecan be chosen in order to get a better light output, the dimension S 101of the light source 1 can be higher.

The optical device 47 can be made of one or several lenses whose opticalplane will preferably be located between the image plane 7 and thesupport 8. It can also be made of an element capable of rendering alight spot created by a converging graduation (such as those seen inrotational encoders) on the support 8, into one series of parallel lightspots 11. It can also be produced by plastic injection moulding. Itallows the adaptation of an integrated circuit into a differentgeometric graduation in an inexpensive manner.

FIG. 8 shows a method of execution for a device working by reflection,including a graduation support 3, a reflecting focusing element 4, alight source 1 and sensitive elements 6. The lines 12 and 13 depicts theenvelope of the useful light flux. The final plane 5 is located behindthe image plane 7 which in this example contains the light source 1 aswell as the sensitive elements 6.

A device working by reflection is more appropriate for use at hightemperatures. For example, polycarbonate loses all its translucentoptical qualities at high temperatures. The use in this example of analuminium graduation support circumvents this drawback. Furthermore, itis easier to assemble the light source 1 jointly with the sensitiveelements 6.

FIGS. 9 a-9 c show the disposition of the sensitive elements on thesupport 8 corresponding to the image plane 7 and a simplifiedrepresentation of the detection circuit for the design of an incrementalmeasuring device whose unit resolution is two times higher than theresolution of the graduation.

In a schematic manner, FIG. 9 a shows a section of the graduationsupport 3, the image plane 7, the sensitive elements 6, and the lightflux 13. Lines 17 show the optical or the division axis and lines 18show the division's boundaries.

The sensitive elements constitute two groups of sensitive elements 6 a/6b and 6 c/6 d which all relate to the same division and which aredisposed geometrically along the projection of at least two divisions 18on the image plane 7. An adequate spacing between the sensitive elementsmust be respected in order to avoid all forms of interaction in theworking of the two neighbouring elements. For example, for a diode ofthe width of 4 μm, there must be a minimal distance between two elementsof 3 μm.

FIG. 9 b shows the disposition of the sensitive elements 6 a, 6 b, 6 c,and 6 d according to FIG. 9 a, the light spots 11 and detection circuits54 a and 54 b for treating a digital signal 23 a which may correspond toan “A” channel. Sensitive elements 6 a, 6 b, 6 c, and 6 d represent aunit of sensitive elements. A first group of sensitive elements 6 a/6 bis connected to detection circuit 54 a and a second group of 6 c/6 d tothe circuit 54 b. The circuits 54 a and 54 b process the signals of analternation which are added or combined in circuit 55 to obtain thedigital signal 23 a. The conversion of the analog signal into a digitalone can be done by the circuits 54 and/or 55. The detection circuit isdenoted by 59 b.

FIG. 9 c shows another configuration of the sensitive elements includinga unit of sensitive elements 56 having the elements 6 a, 6 b, 6 c and 6d and a unit of sensitive elements 57 including elements 6 aa, 6 bb, 6cc and 6 dd. Each unit includes two groups of sensitive elements. Thedistance between the two units will be of a value equal to ⅛ of thelength 21 of the division.

Detection circuit 59 a includes evaluation circuits 58 a,58 b whichprocess an output digital signal 23 ba,23 bb representing the channels“A” and “B” from the point of the current emitted by the two pairs ofdiodes. It can also contain a resolver (not shown), which gives thepossibility to increase the system resolution on the basis of a sinesignal coming from circuit 58 b and a cosine signal coming from circuit58 b and to produce the digital signals 23 ba and 23 bb.

The disposition of the detection circuit 59 b in FIG. 9 b provides anindividual differential measurement for each group of sensitiveelements. The detection circuit 59 a in FIG. 9 c does a differentialmeasurement of the current emitted by each unit of sensitive elementscomprising two groups of sensitive elements. Other dispositions arepossible.

The disposition of the sensitive elements represented in FIG. 9 b hasthe advantage of corresponding to a width of the light spot 11, whichcan be equal to the width of the element. The addition of a second unitof sensitive elements can be done by the disposition of the sensitiveelements along four divisions in one row. It can also be done alongseveral rows.

The disposition of the sensitive elements shown in FIG. 9 c causes aunit of sensitive elements to appear by division which requires adisposition along two rows of sensitive elements. The disposition of thesensitive elements along the same row spread out along several divisionscorresponds to a better light output of the device.

FIG. 10 a refers to the disposition of the sensitive elements which, interms of the invention, presents a favorable alternative design. Theshape of the electric signal coming from the sensitive elements isdefined by the shape and geometric disposition of the diodes 6 a and 6 bas well as the width B,10 of the light spot.

The diodes which correspond to the same division, i.e. 6 a and 6 b, canbe placed side by side or in series divided up over several divisions.The geometric shape of both diodes periodically varies in function ofthe length of the division 21. As the light spots 11 are being shiftedalong the median line 32, these spots will recover (at least along apart of the division) both diodes 6 a and 6 b simultaneously and bothsurfaces delimited by the intersection of the light spot and each of thediodes 6 a and 6 b should substantially vary and generate a usablealternating signal 22.

The minimal width of the light spot B,10 corresponds to a faithfulreproduction of the diodes″ shape which, in some way, is imprinted inthe silicon.

FIG. 10 b shows a type of design suitable for generating sinusshapedsignals, near-sinus shapes for FIG. 10 c, and FIG. 10 c also showsserrated shapes. This last design combined with a graduation made ofjuxtaposed cylindrical lenses would allow the sensor described byKawamura to be improved. FIG. 10 d shows yet other alternative shapes.

In a schematic manner, FIGS. 11 a-11 d show a section of the graduationsupport 3, several different types of optical elements or division 4which are assigned a numerical value of 60, the image plane 7 and thedivision lines 18. The direction of the light flux is representedschematically by arrow 61 directed toward the location of the light spot11.

The optical elements 4 have different shapes and opticalcharacteristics. These correspond to a shape and/or location of a lightspot 11 in relation to the image plane 7 or the perimeter 33 which aredifferent from one division to another and can be detected by thesensitive elements 6.

In a schematic manner, FIG. 11 a shows a portion of graduation support 3containing two types of optical elements with different opticalproperties represented by 61 and which correspond to a binary numericalvalue 27. This is the same for FIG. 11 b and FIG. 11 c which show agraduation comprising a value of base 4 and respectively base 3.

FIG. 11 d shows a variation of the graduation made of two types ofoptical elements with a symmetric focusing portion and an opticalelement without a focusing portion which can represent a transparent,opaque or reflecting section. The difference of the light intensity onthe image plane 7 provides the possibility to detect with the help of agroup of sensitive elements 6 the type of division which is present. Thevalue 60 can have a binary base.

A graduation can contain any amount of different type optical elements.This amount corresponds to the number base of the numerical value of 60.This number is limited by the design and the manufacturing toleranceconsiderations.

In a schematic manner, FIG. 12 a shows a section of the graduationsupport 3, of the asymmetrical optical elements 4 with a binary value of60, of the image plane 7 where four sensitive elements represented by 6are disposed in the projection of four divisions. Lines 18 represent thedivision boundaries and the arrows 61 the direction of the light flux ina schematic manner.

The detection capability of this design corresponds to the fournumerical values within the frame 63 which corresponds to a positionnumber 62 which can be detected by the sensitive elements 6 which canalso correspond to a group or a unit of sensitive elements.

The position number 62 can denote the position of the graduation support3 in relation to the support 8. The length of the position number 62 canbe of any values and depends on the number of divisions analzyed by thesensitive elements on the image plane 7. The analyzed divisions canrefer to one or several graduations.

FIG. 12 b shows the mathematical procedure to conceive an absolutemeasurement device by using only one graduation having two types ofdivision. The disposition of the divisions in numerical value in termsof graduation is shown at 64. Frame 63 will show a 4-bit position number62 moving from top to bottom, which will take a different value for eachposition of the frame as the arrow indicates as shown in column 65. Thesame procedure will be used for a position number with a differentnumber of bits.

FIGS. 13 a and 13 b show a graduation support made of a flask 68 and ofa hub 68. The flask has a graduation 67 made preferably from identicaloptical elements and a second graduation made of graduation segments 66capable of acting as an index. Each segment can contain one or severaloptical elements. A preferred disposition consists in placing severaltypes of optical elements in such a way that each segment corresponds toa position number 62. Each segment preferably has a reference code.

A reference code consists of a graduation made of several types ofoptical elements of which a part is of a particular design which canensure a mathematical base, for example of 2,3, for the reading of theposition number 62. It can be a question of a combination of particularoptical element types. The use of a position number with a number baseof two or three provides the possibility to design such a reference codein a simple manner, reserving for example a digit as a reference pointwhich appears in the position number 62. The reference code can bedisposed in a line or on a distinct graduation.

The advantage of this device is the design of quasi-absolute encoderswhich allows a quick reading of a reference point.

FIG. 14 shows a possible disposition of the sensitive elements and thedesign of the detection circuit for a 9-bit resolution absolutemeasurement device. The device has a graduation 78 which is made ofidentical optical elements and a graduation 79. which is made ofdifferent optical elements. The graduations are represented by the lines18 which represent their projection onto the support 8, a detectioncircuit represented by the elements 76, 72 and 73 which can contain oneor several memory zones, the output lines by 71 a, 71 b, and 71 c andthe internal connections of the detection circuit by 74 a, 74 b, 75 aand 75 b. The value of the position signal of the output lines 71 b and71 c correspond to the digits x0, x1, x2, x3, x4, x5, x6, x7, and x9 ofthe position number 62.

The first graduation 78 is made of identical optical elements. A firstunit of sensitive elements 56 includes a group of sensitive elementscontaining two sensitive elements 6 a and 6 b. A second unit ofsensitive elements 57, brought forward in respect to the first unit by adistance equal to ¼ of the dimension of a division, includes a group ofsensitive elements including two sensitive elements 6 aa and 6 bb.

The second graduation 79 is made of a series of divisions composed oftwo types of different optical elements (FIG. 13 a). The sensitiveelements are distributed into a first group of seven units of sensitiveelements 6 ax corresponding to seven divisions. A second group iscomposed of seven units of sensitive elements which are brought forwardby a distance equal to ¼ of the dimension of a division. It isrepresented by a series of sensitive elements 6 bx.

The sensitive elements of the units 56 and 57 are connected to circuit76 which processes (with a resolver) the digital signals correspondingto the channels “A” and “B”. The detection circuit processes the firstdigits of the position signal 62 which distinguishes the position of thelight spot in terms of the sensitive elements 6 a, 6 b, 6 aa and 6 bb.In this example, they are the first two digits x0 and x1. They couldalso be several digits in function of the resolver-integration rate.

Each group of sensitive elements 6 ax and 6 cx which correspond to adivision is connected to circuit 72 which allows the position of thelight spots to be localised. Each group of sensitive elements relates tothe first position signal 74 a or 74 b processed by circuit 72.

Values 74 a and 74 b are picked up by circuit 73. Each circuit 73receives the signals 75 a and 75 b which can correspond to the outputsignals 71 a or a position signal which help to detect the relativeposition of one division of the graduation 78 in relation to the support8. Each circuit 73 enables to determine by logical analysis thenumerical value of the division with the help of the position signals 74a, 74 b, 75 a and 75 b which are shown by a position signal 62 on theoutput line 71 c following the example in FIG. 14. The operation ofcircuit 73 enables synchronization of the reading of the numericalvalues which correspond to the graduation 79 using position signalscorresponding to the graduation 78.

Each circuit 73 corresponds to a division and a line 71 c for a positionsignal showing a digit “xn” of the position number 62. The graduation 78can correspond to several digits of the position number 62.

The graduation 79 can correspond to several graduations having differenttypes of optical elements. A division of the graduation 79 cancorrespond to several groups of sensitive elements and each group cancorrespond to several sensitive elements.

Each graduation can correspond to several units of sensitive elementswhich can be spread out in several groups along the graduation andseveral sensitive elements can correspond to each group of sensitiveelements and several groups of sensitive elements can correspond to eachunit. The length of division can be different from one graduation toanother.

FIG. 15 a shows the disposition and the procedure allowing the functionof circuits 73 to be formulated.

Rectangles 80 a, 80 b, 80 c and 80 d correspond to sectors appropriatefor the position of the division center of graduation 78 and/or 79. Bothlines 18 show the boundaries of a division in relation to the sensitiveelements 6 a and 6 aa corresponding to the graduation 78, of which thelight flux is shown by the arrow 61 a. The sensitive elements 6 ax and 6aax and light flux 61 b or 61 c correspond to the graduation 79. Thenumerical value attributed to the light flux can be “1” for 61 b and “0”for 61 c.

The sensitive element 6 ax is used for the numerical assessment of thedivision in position 80 a and 80 c, and element 6 cx in positions 80 band 80 d. A position 80 a corresponds to a reversal of the signal 74 a,a position 80 b to a reversal of the signal 74 b, a position 80 c to asame signal 74 a, a position 80 d to a same signal 74 b. The othercombinations are not used. Actually, only a portion of the width of thesensitive elements is in effect used for the determining of the positionnumber 62. The active portion of the sensitive elements 6 ax and 6 cx isshown by the empty rectangle 77 a.

An absolute encoder is complete with a revolution-counting circuit whichis preferably battery powered. Such a counting circuit is not shown inthe above circuit.

FIG. 15 b shows another configuration of the sensitive elements alongthe graduation 79 where a sensitive element 6 ax only corresponds toeach division. The position references 81 a, 81 b, 81 c and 81 dcorrespond to the position references 80 a, 80 b, 80 c, and 80 d in theFIG. 15 a. The same reasoning relating to the logical function ofcircuit 73 can also hold true. At positions 81 b and 81 d, the influenceof the light flux 61 b or 61 c onto one part of the sensitive elementcan produce two different signals 74, which does not guarantee a correctdetection of the position number 62. The active portion of the sensitiveelement 6 ax and 6 cx is shown by an empty rectangle 77 b.

A reduction of the active portion 77 b of the sensitive element 6 axallows these errors to be eliminated. The detection of the divisionvalue 62 is therefore only done in relation to 81 a and 81 c. The valueof the signals 71 c can be recorded in circuit 73. This design presentsa practical disadvantage in that while the current is applied to thedevice, a detection of the absolute position on the points 81 b and 81 dis not guaranteed. It is therefore necessary to obtain the absoluteposition by a small shifting.

Another possibility consists in monitoring the modifications of thenumber's position 62 in several memory registers. A change in positioncan be confirmed or secured on the base of this information. A memorytable can include, for example, three position numbers, the presentvalue and both nearby numbers. The nearby position numbers can becalculated as the need arises. This design can have the disadvantage ofa possible loss of the absolute value.

The disposition of the sensitive elements, the divisions and thenumerical values in the cited examples can be assigned differently.

The adaptation of a circuit integrated to several types of graduation isrelated with complex and expensive development work of integratedcircuit. It would be preferable to design a circuit containing aquantity of sensitive elements which can be linked by bonding ormetallic connections with a single lithographic mask.

FIG. 16 shows a neuronal circuit adaptation to the device which can beused for the making of or a part of a detection circuit. The circuitincludes a neuronal network 148 with the characteristic nodes 149 whichare attached to a circuit 147 which can include a sensitive element 6and produce an output digital signal 159 capable of corresponding to theoutput lines 71 a, 71 b, 74 a and 74 b shown in FIG. 15. Each networknode 149 is linked to its neighboring diode preferably by a resistance150 and toward the mass preferably by a conductance 151. Elements 150and 151 can be one or several resistances and/or transistors preferablyhaving a linear characteristic. The tension of the junction can becarried by one or several circuits not shown in the figure which,failing this, can depend on circuit 147. The choice of the values forconductances and/or resistances are determined for the sensitivity ofthe detection circuit.

Circuit 147 includes a sensitive element generating current 152. Thearrangement of the transistors 161, 162, and 163 generate currents 153and 156 of the same value as of current 152. Current 157 results fromthe sum of the currents given out by the sensitive elements. Thearrangement of transistors 164 and 165 defines the current 154 showingthe difference of the currents 153 and 155 which will be transformed byan evaluation circuit 158 at the threshold level in binary value.

This type of circuit has the advantage of being able to control a largenumber of sensitive elements while, at the same time, being capable ofbeing integrated with the sensitive elements on the same support 8. Thisis particularly useful for the manufacture of an absolute encodercircuit detection.

FIG. 17 a and 17 b show an oscillation device 84 and a procedure tocalculate the average position of the oscillating device 84 and themaximum amplitude of the three last oscillations 85 a, 85 b and 85 c. Arotational register 86 puts the 3 values 85 a, 85 b and 85 c intomemory. The average value of 85 c and 85 a is calculated by circuit 87and the average value between the output of circuit 87 and value 85 bare fed to circuit 88 for the recording of the real value immediatelyafter the recording of a new value 85 c.

This procedure allows a sensor for a rapid reading of the position datato be devised without necessarily having to rely on a damping device.

FIGS. 18 a, 18 b, 18 c, 18 d, 18 e and 18 f show different dispositionsof the light source 1, graduation support 3 corresponding to ahalf-section of a circular support, the graduation 30, optical element91, the light flux 90 and one or several sensitive elements 6.

The advantages of the present invention are as follows:

the design of sensing element for reaching a very high resolution to theorder of 0.0005 angles with a simple circuit,

the design of a sensor whose measurement will be stable in terms oftimes, even during temperature changes and high humidity,

very low frequency resonance

and for use in vehicle movement sensors:

a very accurate measurement of small accelerations to the order of 0.5mg,

a design presenting attractive manufacture costs for the automobileindustry,

and possibility to manufacture a 10 to 16 bit digital potentiometer ofsmall dimensions and at competitive prices.

FIG. 19 shows a gravitational sensor unit with its control circuitcontaining a casing 201, an oscillating mechanical system 231 includingan off-center mass 204 and a disk 202 on which one or severalgraduations 203 can be placed for reading the position or the angulardisplacement of the oscillating system 231 by one or several sensingheads 205.

The oscillating mechanical system 231 is placed on a low-frictionbearing with limited angular movement 207 firmly attached to the shaft208 which forms, via the off-center mass 206, a second oscillatingmechanical system 230 which is placed preferably on two plain bearings209 and 210 being part of the casing 201. The watch maker pivot bearings209 and 210 are part of the casing and are preferably shockproof.

One or several reading heads 250 or groups of sensitive elements 6 areto be placed preferably in an equidistant manner on a circumferencecorresponding to the dimensions of the scale of the division. The shownreading head 250 includes a light source 211, an optical device 220, andone or several sensitive elements placed preferably on an integratedcircuit 205 or support 8.

Two reading heads are to be preferably placed 180° from one another tocompensate for the errors of eccentricity of the graduation of circularscale 203 in relation to the center of rotation of one or several of thesensor's bearings during the reading by counting of the impulses comingfrom the two systems.

The light source 211 may be a light diode or a radioluminessence sourceactivated for example by Tritium which supplies the necessary energy todetect the displacement of the scale 203 by the intermediary of theintegrated circuit 205.

The optical system 220 has the task to ensure an accurate reading of thescale's position. When the scale's division becomes small, the distancebetween the disk and the detection circuit becomes critical. The bondingwires and the mechanical assembly may restrain obtaining of optimalreading conditions. It therefore becomes necessary to introduce, forexample, an optical element composed of one or several lenses projectingthe image of the light flux onto the plane where the sensitive elementsare placed. Another possibility rests in the use of a bunch of opticalfibers containing several optical fibres placed side by side which areto be preferably fixed on or glued to the sensors' surface.

The scale or graduation 203 will be preferably composed of a series ofoptical elements. These optical elements can be made by plasticinjection or mechanical printing in a plastic or metallic support.

It can also be composed of, for example, a metallic pattern applied on apiece of glass or plastic (if possible transparent) at the source of theradiation emitted by the photo-electric source 211. It is also possibleto conceive a scale including a reflector element and/or an alternationof variable-translucent and or different-filtration elements in functionof the light's wavelength and/or transparent focusing optical elements.

The disk 202 of the oscillating sytem 231 can also rest on bearings 209and 210 which however can reduce the mechanical resolution of thesensor. Instead of friction bearings 209 and 210, can be used miniatureroll bearings, ordinary friction bearings and/or bearings controlled bymagnetic suspension, that is, whose position is controlled electrically.The use of bearings made of permanent magnets is also foreseeable withsuitable materials.

The use of several graduation scales 203 has the advantage of easyswitching from one system to another, for example mm/m to an angledegree (360 divisions) or other values without the need to convert thesevalues for example by calculation.

A digital circuit 212 preferably representing a micro-processor systemconnected by one or several conductors 217 to the integrated circuit 205is responsible for the management of the measured values, the opticalindicator display 213 or by acoustic methods 214, the management of oneor several push buttons 215 and other operations to be integrated intothe system. Preferably, a battery 216 should supply the power to theelectric circuit.

FIG. 20 shows a plain bearing, the axis 219 of diameter “d” rests on abearing 218 of diameter “D”. Point 220 a depicts the center of gravityof the oscillating system. Point 222 depicts the maximal position of thecenter of gravity before the sliding of the axis 219 in relation to thebearing 218. Vector 224 shows the weight of the disk “G” and vector 223shows that the maximal friction force equals 1×D/2×G. The value “e”shows the distance between the axis of rotation and the center ofgravity of the oscillating system.

The layout of both vectors show the relation between the forces cominginto action before the sliding of both parts. The extreme position ofthe centre of gravity 222 and the diameter value of the bearing 219 aswell as the friction coefficient determine the minimal angularmechanical resolution of the system which is equal to=2×arctan((10×D)/(2×e)) Where for example, the minimal angular mechanicalresolution of the system has values of D=701m, 1 mo=0.12, e=5 will be0.096 degrees.

Another type of bearing consists of a segmented plain bearing where thecorresponding diameter can be reduced to very small values such as forexample 10 1 m before either the resistance or the manufacturing becomesimpossible. A resolution with the values D=101 m, 1o=0.12, e=5 is 0.014degrees.

Another type of bearing consists of a very low-friction roll bearingwhose minimal angular mechanical resolution is equal to=2×arctan(0.00066*(d/2)/(e)) The minimal mechanical revolution with values ofD=200 μm, d=180 μm, μo=0.12, e=5 is 0.00454 degrees. Other types ofbearings consist of flexible parts preferably a spring allowing themaking of a suspension of a limited angular, low-friction clearance butwhich has the disadvantage of introducing a proportional force in thespring displacement.

The use of a low-friction bearing with a restricted angular movementcombined with a second oscillating system 230 provides the possibilityto keep the advantage of the first name bearing type. The firstoscillating system 231 is conceived in such a way that it can oscillateat an angle value at least higher than the angle value of the angularmechanical resolution of the second oscillating system 230.

FIG. 21 a shows a simple type of roll bearing having an axis 219 onwhich a bearing 218 rests and of which the angular movement is limitedby a pin or a digit 221 firmly attached to the axis 219 capable ofmoving in the interior of the opening 222 firmly attached to the bearing218.

Both rolling surfaces of parts 219 and 218 can be smooth and preferablycompletely or partially geared in such a way that a relative angularsliding of the two oscillating systems can be avoided. Gear cause extrafriction to the detriment of the system's advantages. The use ofinvolute gear with a wide pressure angle could reduce friction. The useof another gear profile can also be envisaged.

FIG. 21 b shows a more rigid solution which develops more frictionincluding an axis 219 of radius “r” and a bearing 218 of radius “R”.This design has the advantage of guaranteeing the angular positionbetween the two oscillating systems 231 and 230. The free movement anglecan be controlled by the bearing or by an extra stop similar to the oneshown in FIG. 23 a.

FIG. 22 shows a disk with preferably constant thickness 225, an axis 226resting in a bearing with a greater diameter, an opening 229 allowingthe displacement of the center of gravity 227 to a distance “e” alongthe axis of rotation of the disk 225 or of the graduation 228,22 whichgives the possibility to assess the disk's angular displacement 225.

The distance of the center of gravity “e” in relation to the center ofrotation of the bearing and the inertia mass of the disk 225 are twoimportant values that define the resonance frequency of the system. Asmall value for “e” reduces the resonance frequency but on the otherhand also reduces the mechanical resolution. For the design of a sensorwith low resonance frequency, it will be necessary to chooselow-friction bearings combined with a second oscillating system.

FIG. 23 schematically shows a electronic-bubble level measuring devicewith a body 232 with a reference surface 234. A gravitational sensor 235as described above will be directly or with the help of an elastic orshockproof mechanism assembled onto the body of the device 232 andelectronically linked up to a detection circuit 236 which, for example,will transmit the measured values to the user via one or severalnumerical display panels 237 and/or one or several acoustic signalelements 251 and/or one or several optical sign elements 252 and/or anadjustable display panel 255.

The display panel 255 can be adjusted manually and/or by means of anoscillating system similar to the oscillating system 231. Thetransmission of the signals for the display of the values can be done bymetallic contacts and/or infrared transmission and/or inductive means.

This measurement device will also be able to measure the inclination ofa plane with regards to the plumb line and/or to compare the inclinationof one plane to another with great precision.

FIG. 24 shows the function diagram of a kilometer recording device asdescribed in the international patent request PCT/EP 93/02415 in FIG. 3a and 3 b comprising a casing 238, a first evaluation unit 239 with asignal input 242 and a circuit for the processing of this signal 243 towhich preferably a kilometre-impulse signal will be connected. A secondevaluation unit 240 having a sensor unit 244, preferably foracceleration sensing, and a circuit for the processing of this signal245, a circuit for comparing the signals 246, a digital circuit (forexample a microprocessor 247), a memory unit 248 and a data output 249for the transfer of the data to the exterior.

The implementation of a gravitational sensor as described above enableto fulfil the conditions required by the device in FIG. 24 in a simplemanner and at low costs. The counting is done in a digital techniquewhich can greatly simplify the working algorithms and reduce thecalculation times for the second evaluation unit 245 as well as theadjoining electronic circuits to be reduced. It has the particularadvantage of being easily calibrated by simply resetting the counter.

The values given by the acceleration sensor 244 and displacement sensor242 that will be transformed by circuits 245 and 243 into accelerationor displacement values are compared in circuit 246. From the fact that avehicle is not always oriented in the horizontal plane, the comparedvalues will have measurement errors. Even so, an analysis of thecomparison values by statistical methods will enable to indicate whetherthe values of the kilometric impulses are constant or correct.

This procedure enables to quantify the value of the received kilometricimpulses in an automatic manner by comparison with the impulse valuesduring the periods of acceleration which will ease the mounting of thedevice on a vehicle. It enables to ensure that the vehicle is sendingthe impulses to the recording system during the displacement of thisand/or whether the value of these impulses is correct or not. Theresulting values are kept in memory and log out at the same time as thekilometric data to a computer station which will evaluate the recordeddata.

The use of a sensor with absolute reading enables to increase thesystem's reliability, which will support its measurements on a unchangedhorizon which increases the reliability of the algorithms used in thecontrol of the recording. The same calculation basis will be remainingeven after a power cut.

FIG. 25 shows an example of an encoder comprising a graduation support 3placed on a tubular shaft 261 in bearings 262, a support 8 where thesensitive elements located on a support 265 are placed, a light source1, a casing 260,263 and ball bearings 262.

What is claimed is:
 1. Method of determining with a light beam one ofthe relative position and the absolute position of a graduation supportin relation to a support with an alternating signal, said alternatingsignal crosses a reference value at least two times, said graduationsupport and said support being displaceable relative to each other indisplacement direction, the method comprising the steps of: producing alight flux by a light source; modifying said light flux by movement ofat least one graduation of said graduation support; providinglight-sensitive elements on said support; intercepting the modifiedlight flux by said light-sensitive elements; and converting intensity ofthe intercepted light flux into an electric signal, wherein: the lightflux is modified by said graduation made of at least one series ofoptical elements, each optical element containing at least one focusingportion; said modified light flux is such that it intercepts at leastthe entire width of an optical element of said at least one series, saidoptical element focusing at least one light spot of said light flux ontosaid support with said light-sensitive elements therein; and said lightflux intercepted by said focusing part of said optical element isconverted into said alternating signal from which said relative positionor said absolute position can be determined whereby a maximum value oflight energy received by at least one light sensitive elementcorresponds to one of a maximum electric signal value and a minimumelectric signal value of said alternating signal.
 2. Method according toclaim 1 wherein a position signal, which depends on a division belongingto said at least one graduation made of several optical elements ofdifferent structure, corresponds to a position number including areference code to show an absolute value of a position between saidgraduation support and said support.
 3. Method according to claim 1where at least one of several position numbers and at least one ofseveral position signals corresponding to the absolute position betweensaid graduation support and said support are stored in a memory tosecure a correct detection of the position number.
 4. Method accordingto claim 1, wherein at least one light spot is produced by said lightflux on said support, said light spot having a shape selected from oneof an oblong shape and a substantially rectangular shape.
 5. Methodaccording to claim 4, wherein at least one first position signal whichdepends on a division belonging to at least one graduation made ofseveral optical elements of different structures, corresponds to asecond position signal which depends on at least one position signalcharacterized by at least one graduation made of optical elements ofidentical structures capable of detecting the relative position of adivision in relation to said support and which depends on said at leastone first position signal, said second position signal corresponding toa digit of a position number to show an absolute value of a positionbetween said graduation support and said support.
 6. Method according toclaim 4, wherein said at least light spot is arranged perpendicularly toa median line of said graduation.
 7. A method according to claim 1,further comprising a step of digitally converting changes of saidalternating signal produced by the relative movement of said graduationsupport and said support and using the digital conversion fordetermining the relative or absolute position.
 8. A method according toclaim 1, wherein focusing is by only the series of optical elements anddivisions.
 9. A device for determining with a light beam one of therelative position and the absolute position of a graduation support inrelation to a support with an alternating signal, said alternatingsignal crosses a reference value at least two times, said graduationsupport and said support being displaceable relative to each other in adisplacement direction along an axis, the device comprising: a lightsource for producing a light flux; a graduation support including atleast one graduation placed in said light flux for modifying said lightflux; at least one light-sensitive element arranged in said support forintercepting said modified light flux, said at least one light sensitiveelement converting intensity of the intercepted light flux into aphysical effect; and a detection circuit for producing an electricsignal from said physical effect, wherein: said graduation is made ofone of at least one series of optical elements and divisions, eachoptical element containing at least one focusing portion; and said lightflux intercepts at least the entire width of an optical element of saidat least one of said series and by focusing produces at least one lightspot on said support with said at least one light sensitive elementtherein; and the detection circuit is designed such that by a relativedisplacement of the graduation support in relation to the support saidalternating signal is produced.
 10. Device according to claim 9, where aprojection surface, which corresponds to the projection surface of saidfocusing portion of said optical element on said support, is greaterthan a surface corresponding to an intersection of the surface of atleast one light-sensitive element and said projection surface, and wherethe width of at least one light-sensitive element is inferior than oneof the width of the projection surface of said focusing portion and thelength of a division.
 11. Device according to claim 9 where said maximumelectric signal value of said alternating signal corresponds to said atleast one of said light-sensitive elements (6 a or 6 a and 6 c) and saidminimal electric signal value of said alternating signal corresponds tosaid at least one of light-sensitive elements (6 b or 6 b and 6 d) whichby the comparison of produced signals by at least two light-sensitiveelements (6 a and 6 b or 6 c and 6 d) can generate an alternating signalwhose value is independent of the light flux produced by said lightsource.
 12. Device according to claim 9, where a division corresponds toseveral light-sensitive elements which are arranged such that each ofthem forms an intersection surface with a perimeter corresponding to atleast one division.
 13. Device according to claim 9, where the width ofthe sensitive element is equal to or corresponds to a multiple of two ofthe length of the graduation.
 14. Device according to claim 9, where adivision corresponds to several groups of sensitive elements so that aunit resolution is greater than resolution of said graduation. 15.Device according to claim 9, which comprises at least a group oflight-sensitive elements and wherein a length which is parallel to adimension perpendicular to a median line, of at least one sensitiveelement, vary in a periodic manner by the length of a division. 16.Device according to claim 9, wherein said at least one sensitive elementis integrated with at least a part of said detection circuit being usedfor treatment of digital and analog signals on said support.
 17. Deviceaccording to claim 9, wherein a section of an image emitted by saidlight source is formed of one of an oblong shape, a rectangular shapeand a shape equivalent to the shape of the sensitive element.
 18. Deviceaccording to claim 9, wherein said light source is placed on one of afinal plane and a plane between the final plane and said graduationsupport, and therefore the width of one or more light spots acting onsaid light sensitive elements can be defined.
 19. Device according toclaim 9, wherein at least two groups of light-sensitive elements areplaced on the same plane at a distance measured parallel to a medianline equal to ¼ of the length of a unit division and wherein said groupsof light-sensitive elements correspond to two signals capable ofdefining a vector, itself defining a circular curve and an angle, whichcan situate with precision the position of said graduation support byevaluating emitted values of said two signals at one of a given pointand a moment.
 20. Device according to claim 1, wherein said graduationsupport is manufactured by injection moulding.
 21. Device according toclaim 1, wherein said graduation support contains at least onegraduation made of optical elements of identical structure whosefocusing portions modify the light flux in such that at least one of theshape and the position of said light spot in relation to a perimeter,which corresponds to a projection surface of the division on thesupport, is identical for each division.
 22. Device according to claim9, wherein said graduation support contains at least one graduation madeof optical elements of different structure whose focusing portionsmodify the light flux such that at least one of the shape and theposition of at least one light spot in relation to a perimeter, whichcorresponds to a projection surface of the division on said support, isdifferent from one division to another which enables assigning anumerical value to one of a type of a division and a type of an opticalelement, said numerical value which can correspond to a selectedmathematical base.
 23. Device according to claim 9, wherein saidgraduation support contains a graduation made of optical elements ofidentical structure and at least a second graduation made of opticalelements of different structure for synchronizing the detection of anumerical value of a division corresponding to a position of the lightspot generated by at least one of several other graduations made ofoptical elements of different structure.
 24. Device according to claim9, wherein said graduation support contains at least a graduation formedby at least one segment of graduation corresponds to at least onereference index.
 25. Device according to claim 9, wherein severalgraduation segments contain a series of optical elements of differentstructure to assign a position number.
 26. Device according to claim 9,wherein at least one optical element of said graduation contains saidfocusing element corresponding to a lens of an essentially cylindricalshape with one of a rectangular base and trapezoidal base.
 27. Deviceaccording to claim 26, wherein the focusing element is curved in thedirection of its length such that a projected image on an image plane isshorter than the length of the optical element.
 28. Device according toclaim 9, wherein at least one optical element of said graduationcontains a focusing element whose optical axis does not correspond to asymmetrical axis of the division.
 29. Device according to claim 9,wherein said graduation support contains at least one of a reflectingelement, the optical elements and said focusing portion, which worksessentially by reflection.
 30. Device according to claims 9, whereinsaid optical element corresponds to a Frensel-, binary- or diffraction-type of lens.
 31. Device according to claim 9, wherein an optical deviceis placed between said graduation support a and said support, saidoptical device projecting an image of an image plane on a planecontaining light-sensitive elements defined by said support.
 32. Deviceaccording to claim 31, wherein said optical device includes a series ofjuxtaposed cylindrical lenses.
 33. Device according to claim 31, whereinsaid optical device includes lenses in different forms having one ofdifferent sections and optical axes allowing the image plane to beformed, in the case of a rotational encoder, of a series of convergingoblong light spots, into a series of at least two light spots which willbe rendered parallel on a support.
 34. Device according to claim 9,wherein the position of the image plane approximately corresponds to amultiple of a focal distance defined by the optical elements.
 35. Deviceaccording to claim 9, wherein at least one of several sensitive elementsand circuits containing at least one sensitive element are joinedtogether by at least one of a conductive element and a resistive elementwhich allows formation of a neuronal circuit.
 36. Device according toclaim 9, wherein said detection circuit corresponds to a graduation madeup of optical elements; of different structure and contains a memoryzone to store at least one of position signals and position numbers. 37.Device according to claim 9, wherein at least one of said graduationsupport and said support contains at least one optical element todeflect the light flux for a more appropriate arrangement of said lightsource and at least one of light-sensitive elements in relation to saidgraduation support.
 38. Device according to claim 9, in combination witha gravitational sensor comprising a casing, a circular graduationsupport whose center of gravity is displaced in relation to a rotationaxis forming an oscillating system; said graduation support including:at least a graduation made of at least one series of optical elements,and light-sensitive elements arranged in said support, said graduationsupport having a center of gravity does not correspond to its center ofrotation, the said support being supported by means of at least onebearing being part of the sensor casing or at least one low-frictionbearing, preferably with limited movement, capable of being part of asecond oscillating system supported by means of at least one bearingpreferably being part of the sensor casing, and preferably an adjustabledisplay panel.
 39. Device according to claim 38, in combination with anelectronic bubble level device to measure the inclination of a surfacein relation to the plumb line which contains said gravitational sensorcontaining a graduation formed of optical elements of differentstructure, and a casing containing a reference surface used as a supportfor measurement of the inclination of a surface.
 40. Device according toclaim 38, wherein the device includes at least one of a visual interfacehaving an LCD display and an auditory interface having an auditoryalarm.
 41. Device according to claim 38 in combination with a device todefine, record, and evaluate data concerning the use of a vehicle whichwill be at least partly directly or indirectly attached to a part of thevehicle, comprising: two independent recording data units; a digitalcircuit including a microprocessor system, for calculation, comparison,and treatment of data coming from at least two recording data units; anda memory unit to store acquired data; and a communication circuitallowing an output of data, wherein one of the two recording data unitsincludes at least said gravitational sensor which provides absolute orrelative reading.
 42. Device according to claim 9, wherein said at leastone light spot is smaller than a surface on said support correspondingto a projection of said at least one focusing portion on said support.43. Device according to claim 9, wherein said graduation support has asurface covered by a reflective layer.
 44. Device according to claim 9,wherein said graduation has optical elements arranged on a circle.
 45. Adevice according to claim 9, wherein changes of said alternating signalproduced by the relative movement of said graduation support and saidsupport is converted to a digital signal and said digital signal is usedfor determining the relative or absolute position.
 46. A deviceaccording to claim 9 wherein-focusing is by only the series of opticalelements and divisions.
 47. Method of determining with a light beam oneof the relative position and the absolute position of a graduationsupport in relation to a support, said graduation support and saidsupport being displaceable relative to each other in displacementdirection, the method comprising the steps of: producing a light flux bya light source; modifying said light flux by movement of at least onegraduation of said graduation support; providing light-sensitiveelements on said support; intercepting the modified light flux by saidlight-sensitive elements; and converting intensity of the interceptedlight flux into an electric signal, wherein: the light flux is modifiedby said graduation made of at least one series of optical elements, eachoptical element containing at least one focusing portion; said modifiedlight flux is such that it intercepts at least the entire width of anoptical element of said at least one series, said optical elementfocusing at least one light spot of said light flux onto said supportwith said light-sensitive elements therein; and said light fluxintercepted by said focusing part of said optical element is convertedinto an alternating signal, said alternating signal crosses a referencevalue at least two times, from which said relative position or saidabsolute position can be determined whereby a maximum value of lightenergy receiyed by at least one light sensitive element corresponds toone of a maximum electric signal value and a minimum electric signalvalue of said alternating signal.
 48. A device for determining with alight beam one of the relative position and the absolute position of agraduation support in relation to a support, said graduation support andsaid support being displaceable relative to each other in displacementdirection along an axis, the device comprising: a light source forproducing a light flux; a graduation support including at least onegraduation placed in said light flux for modifying said light flux; atleast one light-sensitive element arranged in said support forintercepting said modified light flux, said at least one light-sensitiveelement converting intensity of the intercepted light flux into aphysical effect; and a detection circuit for producing an electricsignal from said physical effect, wherein: said graduation is made ofone of at least one series of optical elements and divisions, eachoptical element containing at least one focusing portion; said lightflux intercepts at least the entire width of an optical element of saidat least one of said series and by focusing procedures at least onelight spot on said support with said at least one light sensitiveelement therein; and the detection circuit is designed such that by arelative displacement of the graduation support in relation to thesupport an alternating signal, which crosses a reference value at leasttwo times, is produced.